The present invention relates to a liquid crystal polyester. More specifically, it relates to a liquid crystal polyester resin having excellent colorability, improved heat resistance and high mechanical properties.
A thermotropi liquid crystal polyester resin (to be referred to as xe2x80x9cliquid crystal polyester resinxe2x80x9d or abbreviated as xe2x80x9cLCPxe2x80x9d hereinafter) is increasingly used in not only molded articles but also fibers and films due to its excellent mechanical properties such as heat resistance and stiffness, chemical resistance and dimensional stability. Particularly in information and communication fields such as personal computers and portable telephones, parts are becoming more highly integrated, smaller in size and thickness, and lower in height rapidly, there are many cases where an extremely thin portion having a thickness of 0.5 mm or less is formed, and the consumption of the liquid crystal polyester resin is greatly expanding due to its characteristic properties such as excellent moldability, that is, flowability and the formation of no flash which is not seen in other resins.
Meanwhile, many proposals have been made for further improvement of suchproperties as flowability, heat resistance and mechanical properties at the time of polymerization of a liquid crystal polyester resin composition. JP-A 8-511573 (the termxe2x80x9cJP-Axe2x80x9d as used herein means anxe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a liquid crystal polyester resin composition which is produced by containing an alkali metal in a specific monomer and copolymerizing it and has improved heat resistance.
However, there is still room for the improvement of color uniformness and color strength on coloring the liquid crystal polyester resin composition by a colorant such as carbon black or azo pigment and use thereof in fields that require color uniformness and color strength on coloring is limited.
Then, a liquid crystal polyester resin which has excellent colorability, improved heat resistance and high mechanical properties has been desired.
The inventors of the present invention have conducted intensive studies and have found that a liquid crystal polyester resin having excellent colorability, improved heat resistance and high mechanical properties is obtained by copolymerizing a trace amount of 4-hydroxyisophthalic acid and/or salicylic acid with another polymerizable monomer and containing a specific amount of an alkali metal ion in the copolymer. The present invention has been accomplished based on this finding.
That is, the present invention provides a liquid crystal polyester resin which comprises 1 to 500 mmol % of a recurring unit derived from 4-hydroxyisophthalic acid and/or salicylic acid as a comonomer and 10 to 5,000 ppm in terms of an alkali metal of an alkali metal compound. This resin is a liquid crystal polyester resin which has excellent colorability, improved heat resistance and high mechanical properties and solves the above problems.